1. Field of the Invention
The present invention relates to a resin for toner, toner using the resin, and development agent using the toner.
2. Description of the Background Art
Binder resins account for 70% or more of conventional toner, and most of the binder resins derive from petroleum. This creates concerns about depletion of oil reserves and global warming caused by emission of carbon dioxide into the air resulting from mass consumption of oil.
Accordingly, toner made of resins such as poly-lactates deriving from plants has been proposed to deal with such concerns, because plants grow by taking in carbon dioxide from the atmosphere, thereby solving both problems of global warming and oil depletion.
However, poly-lactate is highly crystalline if it contains only L-lactate or D-lactate. Such poly-lactate is extremely insoluble in organic solvents, which makes it difficult to use toner manufacturing methods such as dissolution resin suspension methods.
Japanese patent application publication no. 2008-262179 (JP-2008-262179-A) describes a method of improving the solubility of poly-lactate in organic solvents by mixing L-lactate and D-lactate to decrease the crystallinity of the poly-lactate.
However, the glass transition temperature of poly-lactate is 60° C. or lower, and using poly-lactate singly further lowers the glass transition temperature and the heat distortion temperature due to moisture absorption. Therefore, if such poly-lactate is transported or preserved under high-temperature and high-humidity conditions, particles or formed images conglutinate to an impermissible level.
Therefore, modification of poly-lactate is required to use it as a binder resin for toner. With regard to this point, JP-H08-302003-A describes manufacturing of copolymerized poly-lactates by reacting a reactant of an aromatic dicarboxylic acid and an aliphatic diol with lactic acid. However, since the glass transition temperature of the thus-obtained poly-lactate is still 60° C. or lower, it remains difficult to transport or preserve toner formed of poly-lactate under high-temperature and high-humidity conditions.
In addition, JP-2007-112849-A describes a method of synthesizing a copolymerized poly-lactate into which a fluorene skeleton is introduced to raise the glass transition temperature to 60° C. or higher. However, since fluorene tends to be fluorescent under irradiation by ultraviolet light, it is not suitable as a resin for toner.
Furthermore, JP-H11-327209-A describes a method of developing toner having excellent heat resistance while keeping a good low temperature fixing property by having a branch skeleton in the polymer chain. However, this is not applied to poly-lactates but to polymers formed of styrene-based monomers and acrylic-based monomers.